The invention relates to a pointed heat-generating device for molds of injection molding machines.
The pointed heat-generating device is used widely for runnerless injection molding machines in order to fuse instantaneously synthetic resin existing at an injection gate communicating to a cavity of the molds, to open the injection gate and to inject the fused synthetic resin into the cavity.
A conventional pointed heat-generating device for molds of injection molding machines is disclosed in Japanese Pat. No. 902601, the corresponding U.S. Pat. No. 3,800,027, U.K. Pat. No. 1,382,800, German Pat. No. 2207001, French Pat. No. 72 05. 125, etc.
The above conventional heat-generating device is provided at its pointed end with such a heat-generating wire as a nichrome wire, wherein the heat-generating wire is generated intermittently in synchronization with an injection molding cycle. When carrying out an injection molding of glass fiber containing synthetic resins in accordance with this process, the heat-generating wire is inclined to be worn. Further, there exists a twice-folded nichrome wire as a heat-generating member in order to reinforce its wear resistance. However, the heat-generating effect of the twice-folded nichrome wire is inferior to the aforementioned normal one.
For the purpose of eliminating the disadvantages of the prior art, the inventor of the present patent application invented a pointed heat-generating device shown in FIG. 1. It is disclosed in Japanese Unexamined Utility Model Publication No. 56-55631 (corresponding to Japanese Utility Model application No. 54-136755) which was laid open for public inspection on May 14, 1981.
In FIG. 1, there is mounted a coiled heat-generating means II within a pointed section Ia of a heat-generating device I. Its heat generation is quite sufficient and its wear resistance is also improved. Nevertheless, the pointed section Ia is large at size and the heat-generating device I itself is elongated. Accordingly, a heating response due to the increase of heat capacity and a cooling response due to a switching operation are not carried out suitably.